A motor with built-in permanent magnets is widely known as an electromotive element of a sealed compressor. The motor with built-in permanent magnets includes a stator fixed to a sealed container, a rotor located inside the stator, including a plurality of electromagnetic steel plates stacked on each other, and in which permanent magnets are inserted, and a rotary shaft fixed to the rotor and connected to a compression element. When a current is applied to the stator, a rotating magnetic field is generated by the stator. The rotor rotates owing to attracting and repelling action between the rotating magnetic field and the permanent magnet of the rotor, and thus a crank shaft fixed to the rotor is caused to rotate. Consequenity, the compression element of the compressor connected to an eccentric shaft portion of the crank shaft compresses refrigerant.
The refrigerant in the compressor is sucked through a suction port and compressed by the compression element, and then passes through a gap between the motor, which is the electromotive element, and the shell, or a refrigerant flow path provided in the stator, and is discharged through a discharge port. In addition, a refrigerant flow path may also be formed in the rotor, to allow the refrigerant to flow through in the axial direction. The refrigerant flow path formed in the rotor not only serves as a route for the compressed refrigerant to proceed to the discharge port of the compressor, but also serves to cool the motor rotor in the compressor, which generates heat during the operation. More specifically, the rotor generates heat owing to eddy current on the magnet surface generated when the rotating magnetic field interlinks with the permanent magnet. In addition, the magnetic flux amount and demagnetization resistance of the permanent magnet is dependent on temperature, and the demagnetization resistance decreases as the temperature increases. To solve the problem, techniques to improve the heat dissipation performance of the rotor by causing the refrigerant to flow through the rotor have been proposed (see, for example, Patent Literatures 1 and 2).
Patent Literature 1 discloses a rotor in which the end openings of the refrigerant flow path in the axial direction are formed with a phase difference in a positive direction and a negative direction, to improve the cooling effect of the refrigerant flow path to cool the rotor. Electromagnetic steel plates are stacked by a phase difference of 180 degrees to allow the openings shifted in the positive direction and the negative direction to communicate with each other to form projections and recesses on the surface of the flow path. Patent Literature 2 discloses a rotor in which the electromagnetic steel plates include a flow path formed on a radially inner side of the rotor to extend in the axial direction and a flow path extending radially inward from the outer circumference of the rotor, and are stacked by a phase difference to allow the flow path on the radially inner side of the electromagnetic steel plate and the flow path extending radially inward from the outer circumference to communicate with each other.